1. Field of the Invention:
This invention relates to optical tracers and in particular to improved acceleration deceleration circuits for such tracers.
2. Description of the Prior Art:
Optical pattern tracers are well known in the machine tool field and are commonly used to control the cutting of various machine tools, particularly gas and some cutting machines, which may be caused to cut specific shapes from material based upon a predetermined optical pattern. One class of such pattern tracers is an optical pattern tracer which views a pattern such as a dark silhouette or line on a white surface and causes the tracer and its associated machine tool to follow the convolution of the pattern. One of the preferred forms of optical tracers, scans a circular area repetitively across the edge of the pattern and producing an electrical signal representative of the change of reflectance as the scanning action crosses the edge of the pattern. This electrical signal is then used together with reference signals and other information to produce coordinate drive information to control X and Y drive motor which cause the machine to move with constant tangential velocity around the pattern. Typical of tracers of this class are those described in U.S. Pat. No. 3,704,372, issued Nov. 28, 1972 to Robert E. Parker, et al., U.S. Pat. No. 3,727,120, issued Apr. 10, 1973 to George Jewell, et al., U.S. Pat. No. 3,860,862, issued Jan. 14, 1975 to William Dell, et al., and U.S. Pat. No. 3,883,735, issued May 13, 1975 to Francis P. Murphy, et al.
In many such tracers the tracing velocity is changed not only at the beginning and end of a trace, but also during certain convolutions, for example, on certain corners and at times when other procedures are required. This slowdown may be initiated either by a special mark on the pattern or by the mere existence of a rapid change of direction or, in the simplest form, such a slowdown may be initiated by the operator by operating operation of a suitable switch, pushbuttom, etc.
In all of these situations, the change in velocity tends to be a step function, abruptly changing from one velocity to a higher or lower velocity. It will be obvious that such step changes in the velocity may cause the machine to vibrate or shake, due to the demand for maximum acceleration or deceleration. Such vibrations will cause imperfections in the cut or tracing action.